date:Univ Louvain, Dept Chem, B-3001 Louvain, Belgium; HoChiMinh City Univ Technol, Grp Computat Chem, Fac Chem Engn, Thanh Pho Ho Chi Minh, Vietnam; Univ Danang, Fac Chem Engn, Danang, Vietnam; Univ Technol & Econ, Dept Inorgan Chem, H-1521 Budapest, Hungary
Quantum chemical calculations using molecular orbital (HF, CASSCF) and density functional theory (B3LYP) methods, in conjunction with the 6-311+ +G(d,p) basis set, have been applied to investigate the molecular and electronic structure of two diamino-meta-quinonoid molecules 1a and 2a , each containing a six-membered ring coupled with two exocyclic C=O bonds situated in a meta position, along with two amino substituents (NH2 and NH-CH3). It is confirmed that these substituted meta -quinone systems exhibit a zwitterionic structure in which the positively charged N-C-C(H)-C-N subunit, containing the two amino-groups, forms two chemical bonds with the negatively charged O-C-C(H)-C-O subunit. The negative charge amounts to about half of an electron. The charge separation has been approached in terms of geometries, vibrational frequencies, and electronic distribution. The ionization energy for molecule 1a is about 7.8+/-0.3 eV. The quinonoid systems are essentially non-aromatic characterized by the NICS(+1) values of around 1.2 ppm.